1. Field of the Invention
The present invention generally relates to a curable sealer and/or adhesive composition having improved compatibility with wet base coat paints. The invention also relates to a method, and the coated substrates formed by the method, where a base coat paint is coated over such a curable sealer/adhesive composition in a wet state to provide a base coat paint, upon drying, having reduced surface defects.
2. Description of the Related Art
It has been observed that certain conventional seam sealers based on polyethers having hydrolyzable silicon-containing end groups have exhibited a compatibility problem with some automotive aftermarket base coat paints when the base coat is applied onto the fresh (wet) sealer. Examples of such conventional seam sealers are described, for example, in U.S. Pat. Nos. 3,971,751 to Isayama et al. and 4,444,974 to Takase et al. The problem that can occur in use of these conventional seam sealers manifests itself as, at one extreme, a gross failure of the paint to even wet the fresh (wet) sealer. On the other hand, even the base coats which wet the seam sealer often experience cracking and/or a light or "feather edge" phenomena characterized by the paint wrinkling and shrinking slightly away from the edge of the sealer to leave a fine unpainted edge of the sealer. All of these prior base coat defects, including the feather edge problem, are unacceptable in many applications.
The feather edge phenomena is more likely to occur where a sealer bead has been tooled or feathered out, as is typically the case, before application of the base coat thereto. As one specific example, this feather edge problem is seen where the above-mentioned conventional seam sealers are spray painted within 60 minutes with a base coat, especially a base coat based on acrylic resins.
Although these base coat problems feasibly could be avoided if the sealer was permitted to dry to complete cure (at least about 24 hours) before application of the base coat thereto as a wet-on-dry scenario, such a delay naturally would significantly lower productivity and convenience in completing the paint operation as well as creating its own problems, such as a poor paint adhesion of acrylic-based paints to a precured (dried) seam sealer.
It is also feasible to cosmetically mask these cracking and wrinkling defects occuring in the base coats applied over the mentioned conventional seam sealers by applying a relatively thick succession of overcoats with long flash times to the extent necessary to smooth out the replications from the original defect-ridden surface of the base coat. However, in addition to the nuisance and added cost and time of this possible corrective measure, it ultimately may not succeed in all instances in any event, such as where the original surface defects in the base coat are particularly profound. Further, the resulting thickened overall coating layer itself can be expected to be more susceptible to failure, such as cracking, peeling and flaking, than if thinner overcoats could have been utilized in forming the multi-coat paint layering system.
Also, from a practical and productivity standpoint, it is highly desired in the field to apply paint coatings in flashes at relatively short intervals of 2-10 minutes. Therefore, the resort to long flash times in order to create thickened coatings in an attempt to mask any underlying surface defects may not be tolerable in many situations.
As can be understood from the above, the formulations of conventional seam sealers having silicon containing hydrolyzable end groups which have been proposed to date, have disadvantages and as yet unsolved problems when used in conjunction with base coats such as acrylic base coats.